Terminal station apparatus, base station apparatus, transmission method and control method

ABSTRACT

A terminal apparatus includes circuitry and a transmitter. The circuitry, in operation, generates a reference signal using a cyclic shift value and an orthogonal sequence, which are associated with each other. The orthogonal sequence is one of two orthogonal sequences corresponding to a first orthogonal sequence [1, 1] and a second orthogonal sequence [1, −1]. The cyclic shift value is one of 12 cyclic shift values ranging from 0 to 11. The transmitter, in operation, transmits the reference signal multiplexed with a data signal. Two of the cyclic shift values having a difference of 6 are respectively associated with the two orthogonal sequences.

BACKGROUND Technical Field

The present invention relates to a terminal station apparatus, a basestation apparatus, a transmission method and a control method.

Description of the Related Art

3GPP LTE (3rd Generation Partnership Project Long-term Evolution,hereinafter referred to as “LTE”) uplink uses cyclic shift sequences,which are orthogonal sequences, as pilot signals to reduce interferenceamong sequences. A cyclic shift sequence can be generated by cyclicallyshifting a pilot sequence by a cyclic shift amount on the time axis. Forexample, FIG. 1 shows a cyclic shift sequence (m=0) and a cyclic shiftsequence (m=1) with pilot sequence length N=12 and cyclic shift amountΔ=6.

In FIG. 1, while the cyclic shift sequence (m=0) is configured in orderof a(0) to a(11), the cyclic shift sequence (m=1) is configured, bycyclically shifting the cyclic shift sequence (m=0) by Δ(=6) samples, inorder of a(6) to a(11), a(0) to a(5).

The cyclic shift amount is determined by a base station apparatus(hereinafter abbreviated to “base station”) and reported from the basestation to a terminal station apparatus (hereinafter abbreviated to“terminal”) per scheduling (per subframe). Eight types “0, 2, 3, 4, 6,8, 9, 10” (3 bits) are defined for reporting the cyclic shift amount.These correspond to a cyclic shift amount of “0, 2, 3, 4, 6, 8, 9,10”×symbol length/12 (ms).

Since sequences can be separated with low inter-sequence interference byassigning cyclic shift sequences of different cyclic shift amounts todifferent terminals, cyclic shift sequences are used for pilot signaltransmission in MU-MIMO (Multiple User-Multiple Input Multiple Output).In MU-MIMO, a plurality of terminals transmit data signals at the sametime and the same frequency, spatially multiplex the data signals andthereby improve system throughput. At this time, it is also preferablethat a plurality of terminals transmit pilot signals at the same timeand the same frequency from the standpoint of frequency utilizationefficiency. Therefore, cyclic shift sequences, which are orthogonalsequences, for pilot signals and the cyclic shift sequences aretransmitted at the same time and the same frequency. The reception sidecan separate pilot signals using the nature of orthogonal sequences, andcan thereby accurately estimate a channel state of each terminal.

On the other hand, in LTE-Advanced (hereinafter referred to as “LTE-A”)uplink, studies are being carried out on supporting SU-MIMO (SingleUser—Multiple Input Multiple Output) to improve throughput, whereby oneterminal transmits data signals from a plurality of antenna ports at thesame time and the same frequency and spatially multiplexes the datasignals using virtual communication channels (hereinafter referred to as“streams”) in the space.

Here, the “antenna port” refers to a logical antenna (antenna group)made up of one or a plurality of physical antennas. That is, the antennaport does not always refer to one physical antenna, but may also referto an array antenna made up of a plurality of antennas. For example, theantenna port may be made up of a plurality of physical antennas anddefined as a minimum unit whereby a base station or terminal cantransmit different pilot signals. Furthermore, the antenna port may alsobe defined as a minimum unit for multiplying a weight of a precodingvector. Hereinafter, a case will be described as an example where an“antenna port” and a physical antenna have a one-to-one correspondencefor simplicity of explanation.

SU-MIMO requires pilot signals for each stream and studies are beingcarried out on code-multiplexing pilot signals of each stream using acyclic shift sequence, which is an orthogonal sequence, for the purposeof reducing inter-sequence interference.

Here, in an ideal environment in which there is no channel variation, acyclic shift sequence is an orthogonal sequence and no inter-sequenceinterference occurs. On the other hand, in a real environment with achannel variation, complete orthogonality is not established and acertain degree of inter-sequence interference occurs. Especially whenthe number of streams increases and the cyclic shift sequencemultiplexing number increases, inter-sequence interference alsoincreases. Therefore, in LTE-A, studies are being carried out onreducing inter-sequence interference using a Walsh sequence as well ascyclic shift sequences adopted in LTE.

In multiplexing using Walsh sequences, pilot signals of a first slot(slot #1) and a second slot (slot #2) making up a subframe aremultiplied by Walsh sequence w1=[1 1] or Walsh sequence w2=[1−1] (seeFIG. 2). That is, Walsh sequence w1 uses pilot signals similar to thoseconventional ones in first and second slots and Walsh sequence w2 usespilot signals similar to those conventional ones in the first slot anduses pilot signals with an inverted phase (180 degree rotation) in thesecond slot.

As a method of reporting a cyclic shift amount, in LTE, the base stationreports in three bits using a control information channel (PhysicalDownlink Control Channel, PDCCH) to be reported to each terminal perscheduling. Furthermore, in LTE-A, studies are being carried out onadding one bit indicating whether a Walsh sequence of each terminal isw1 or w2 using a control information channel (PDCCH), the base stationreporting the Walsh sequence to each terminal and each terminalswitching between the Walsh sequences.

Furthermore, in order to reduce inter-sequence interference of cyclicshift sequences between streams in SU-MIMO, Walsh sequence w1 is usedfor pilot signals of odd-numbered streams and Walsh sequence w2 is usedfor pilot signals of even-numbered streams (see FIG. 3).

Here, the “stream number” is a number indicating order in which data isassigned. For example, when data is transmitted with only one stream,suppose a stream transmitted from one antenna port is stream #0 and whendata is transmitted with two streams, the stream transmitted from anantenna port different from the above-described port is stream #1. Bysetting different Walsh sequences depending on whether a stream numberis an odd number or even number, it is possible to reduce inter-sequenceinterference between pilot signals of neighboring streams (seeNon-Patent Literature 1). Furthermore, since there is no need forreporting a bit indicating a Walsh sequence, which will be used in thesecond (stream #1) and subsequent streams, the amount of reporting thecyclic shift amount can be reduced.

CITATION LIST Non-Patent Literature

Non-Patent Literature 1: R1-091772: Reference Signal structure forLTE-Advanced UL SU-MIMO, 3GPP TSG RAN WG1 Meeting #57, San Francisco,USA, May 4th-8th, 2009

BRIEF SUMMARY Technical Problem

However, when simultaneous application of SU-MIMO and MU-MIMO isconsidered aiming at a further throughput improvement, inter-sequenceinterference occurs between pilot signals among terminals in addition tointer-sequence interference between a plurality of pilot signals used bythe same terminal. For example, as shown in FIG. 4, when the firstterminal (UE (User Equipment)#1) uses Walsh sequence w1 in a firststream (stream #0) and uses Walsh sequence w2 in a second stream (stream#1), the second terminal (UE#2) uses Walsh sequence w1 in the firststream (stream #0), the first stream of the first terminal receivesinter-sequence interference from two pilot signals; the second stream ofthe first terminal and the first stream of the second terminal.Furthermore, as shown in FIG. 5, when the first terminal and the secondterminal have different transmission bandwidths, inter-sequenceinterference further increases.

For such a situation in which both SU-MIMO and MU-MIMO are applied, theprior art cannot sufficiently reduce inter-sequence interference.

It is an object of the present invention to reduce inter-sequenceinterference in pilot signals between terminals while suppressinginter-sequence interference in a plurality of pilot signals used by thesame terminal even when SU-MIMO and MU-MIMO are simultaneously applied.

Solution to Problem

A terminal station apparatus according to the present invention includesa reception section that receives assignment control informationreported with downlink resources, a determining section that determinesWalsh sequences of first and second stream groups at least one of whichincludes a plurality of streams based on the assignment controlinformation; a formation section that forms a transmission signal byspreading each stream included in the first and second stream groupsusing the determined Walsh sequences and a transmission section thattransmits the formed transmission signal, wherein mutually orthogonalWalsh sequences are set in the first and second stream groupsrespectively and users are assigned in the stream group units.

A base station apparatus according to the present invention includes acontrol section that sets mutually orthogonal Walsh sequences in firstand second stream groups at least one of which includes a plurality ofstreams and assigns users in the stream group units and a transmissionsection that transmits assignment control information indicating theWalsh sequence set in the first or second stream group.

A transmission method according to the present invention includes areception step of receiving assignment control information transmittedwith downlink resources, a determining step of determining Walshsequences of first and second stream groups at least one of whichincludes a plurality of streams, based on the assignment controlinformation, a forming step of forming a transmission signal byspreading streams included in the first or second stream group using thedetermined Walsh sequences and a transmission step of transmitting theformed transmission signal, wherein mutually orthogonal Walsh sequencesare set in the first and second stream groups respectively and users areassigned in the stream group units.

A control method according to the present invention includes a controlstep of setting mutually orthogonal Walsh sequences in first and secondstream groups, at least one of which includes a plurality of streams andassigning users in the stream group units, and a transmission step oftransmitting assignment control information indicating the Walshsequences set in the first or second stream group.

Advantageous Effects of Invention

According to the present invention, it is possible to reduceinter-sequence interference in pilot signals between terminals whilesuppressing inter-sequence interference in a plurality of pilot signalsused by the same terminal to a low level even when SU-MIMO and MU-MIMOare simultaneously applied.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a diagram illustrating a cyclic shift sequence (m=0, 1) whencyclic shift amount Δ=6;

FIG. 2 is a diagram illustrating a multiplexing method using Walshsequences;

FIG. 3 is a diagram illustrating a correspondence relationship between astream number and a Walsh sequence;

FIG. 4 is a diagram illustrating inter-sequence interference that occursbetween terminals in MU-MIMO;

FIG. 5 is a diagram illustrating inter-sequence interference that occursbetween terminals when transmission bandwidths are different in MU-MIMO;

FIG. 6 is a diagram illustrating the applicability in SU-MIMO andMU-MIMO;

FIG. 7 is a diagram illustrating a configuration of a base stationaccording to Embodiment 1 of the present invention;

FIG. 8 is a diagram illustrating an example of a correspondencerelationship between a stream number and a Walsh sequence;

FIG. 9 is a diagram illustrating a configuration of a terminal accordingto Embodiment 1;

FIG. 10 is a diagram illustrating another example of a correspondencerelationship between a stream number and a Walsh sequence;

FIG. 11 is a diagram illustrating an example of a correspondencerelationship between a stream number and a cyclic shift amount;

FIG. 12 is a diagram illustrating an example of an operating sequenceidentification table;

FIG. 13 is a diagram illustrating another example of an operatingsequence identification table;

FIG. 14 is a diagram illustrating further candidates for pairs of acyclic shift amount and a Walsh sequence;

FIG. 15 is a diagram illustrating advantages when an interval betweencyclic shift amounts in first and second streams is set to a maximum;

FIG. 16 is a diagram illustrating candidates for pairs of a cyclic shiftamount and a Walsh sequence;

FIG. 17 is a diagram illustrating other candidates for pairs of a cyclicshift amount and a Walsh sequence;

FIG. 18 is a diagram illustrating still further candidates for pairs ofa cyclic shift amount and a Walsh sequence;

FIG. 19 is a diagram illustrating still further candidates for pairs ofa cyclic shift amount and a Walsh sequence;

FIG. 20 is a diagram illustrating an example of a correspondencerelationship between a stream number and a cyclic shift amount;

FIG. 21 is a diagram illustrating another example of an operatingsequence identification table according to Embodiment 3; and

FIG. 22 is a diagram illustrating a correspondence relationship betweena cyclic shift amount and a Walsh sequence set in second to fourthstreams.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings.

Embodiment 1

Viewpoints of the present invention will be described first, beforedescribing a more specific configuration and operation of an embodiment.

In SU-MIMO, one terminal simultaneously transmits data signals using aplurality of streams. Here, suppose “streams” are signals transmittedfrom antenna ports associated with data signals or pilot signals (orcommunication channel in the space). Streams are also called “layers.”Furthermore, in vectors (precoding vectors) used for weight controlunder study for demodulation pilot signals on an LTE-A uplink, streamsand precoding vectors are associated in a one-to-one correspondence.

On the other hand, in MU-MIMO, a plurality of terminals transmit datasignals with one or a plurality of streams simultaneously.

At this time, in SU-MIMO, inter-sequence interference of pilot signalsincreases as the number of streams per terminal increases, while inMU-MIMO, inter-sequence interference of pilot signals increases as thenumber of streams per terminal or the number of spatially multiplexedterminals increases.

Therefore, in a situation in which both the number of streams perterminal and the number of spatially multiplexed terminals are large,inter-signal interference of data signals and pilot signals increasesand the error rate deteriorates considerably. Therefore, the possibilitythat such a situation may be used in a real environment is low (see FIG.6) and even if performance is improved for such a situation,contribution of the amount of performance improvement to the entiresystem is considered small.

Furthermore, in LTE-A uplink, studies are being carried out on SU-MIMOtransmission using four antennas for transmission and receptionrespectively as a spatial multiplexing number which can be realized in areal environment, that is, MIMO transmission having a maximum number ofstreams of 4. Based on SU-MIMO, a maximum number of streams of 4 islikewise a spatial multiplexing number that can be realized in a realenvironment also in MU-MIMO transmission. Therefore, a case will bestudied below as an example where the number of streams per terminal inSU-MIMO is a maximum of 4 or less or the total number of streams perterminal in MU-MIMO is 4 or less.

[Configuration of Base Station Apparatus]

FIG. 7 is a diagram illustrating a configuration of base station 100according to the present embodiment.

Coding section 101 receives transmission data (downlink data), aresponse signal (ACK/NACK signal) inputted from error detection section117, resource assignment information of each terminal inputted fromscheduling section 109, control information indicating MCS (ModulationCoding Scheme) or the like, weight control information for controllingtransmission power/weight, information on cyclic shift amounts,information indicating a correspondence relationship between a cyclicshift amount (or stream number) and a Walsh sequence or the like asinput. Information on the correspondence relationship between a streamnumber and a Walsh sequence will be described later.

Assignment control information is composed of a response signal,resource assignment information, control information, weight controlinformation, information on cyclic shift amounts, information on thecorrespondence relationship between a stream number and a Walsh sequenceor the like. Coding section 101 codes the transmission data andassignment control information and outputs the coded data to modulationsection 102. The information on the cyclic shift amount, assignmentcontrol information including information indicating the correspondencerelationship between a stream number and a Walsh sequence aretransmitted per scheduling from RF (Radio Frequency) transmissionsection 103, which will be described later.

Modulation section 102 modulates the coded data inputted from codingsection 101 and outputs the modulated signal to RF transmission section103.

RF transmission section 103 applies transmission processing such as D/A(Digital to Analog) conversion, up-conversion, amplification to thesignal inputted from modulation section 102 and transmits by radio thesignal subjected to the transmission processing from one or moreantennas to each terminal.

RF reception section 104 applies reception processing such asdown-conversion, A/D (Analog to Digital) conversion to a signal receivedvia an antenna from each terminal and outputs the signal subjected tothe reception processing to separation section 105.

Separation section 105 separates the signal inputted from RF receptionsection 104 into a pilot signal and a data signal. Separation section105 outputs the pilot signal to DFT (discrete Fourier transform) section106 and outputs the data signal to DFT section 111.

DFT section 106 applies DFT processing to the pilot signal inputted fromseparation section 105 and converts the signal from a time-domain signalto frequency-domain signal. DFT section 106 then outputs the pilotsignal converted to the frequency-domain signal to demapping section107.

Demapping section 107 extracts a pilot signal of a portion correspondingto a transmission band of each terminal from the frequency-domain pilotsignal inputted from DFT section 106. Demapping section 107 then outputseach extracted pilot signal to estimation section 108.

Estimation section 108 determines a sequence of pilot signals received,based on a cyclic shift amount and a Walsh sequence (w1 or w2) inputtedfrom pilot information determining section 110 as information on thesequence of pilot signals.

Furthermore, estimation section 108 extracts a desired pilot signal fromthe pilot signals inputted from demapping section 107 using informationon the sequence of the pilot signals and acquires estimate values byestimating a frequency-domain channel state (channel frequency response)and reception quality. Estimation section 108 then outputs the estimatevalue of the channel frequency response to signal separation section 113and outputs the estimate value of the reception quality to schedulingsection 109.

Scheduling section 109 schedules assignment of a transmission signaltransmitted by each terminal to a transmission band (frequency resource)according to the estimate value of the reception quality inputted fromestimation section 108. Scheduling section 109 also determinestransmission power/weight of the transmission signal transmitted by eachterminal. Scheduling section 109 outputs assignment control information(e.g., resource assignment information, control information) indicatingthe scheduling result and weight control information for controllingtransmission power/weight to coding section 101 and outputs resourceassignment information to pilot information determining section 110.

Pilot information determining section 110 determines a transmission bandof a pilot signal, based on the resource assignment information inputtedfrom scheduling section 109. Furthermore, pilot information determiningsection 110 stores a plurality of correspondence relationships between astream number and a Walsh sequence and selects a correspondencerelationship between a stream number and a Walsh sequence that canreduce inter-sequence interference between pilot signals from among theplurality of correspondence relationships.

FIG. 8 is a diagram illustrating an example of a correspondencerelationship between a stream number and a Walsh sequence stored inpilot information determining section 110. In the example shown in FIG.8, two patterns; pattern A and pattern B are shown as the correspondencerelationship between a stream number and a Walsh sequence. Pilotinformation determining section 110 assigns, in the case of MU-MIMO, forexample, pattern A and pattern B to a terminal to be multiplexed andoutputs information indicating a correspondence relationship between astream number indicating pattern A or pattern B and a Walsh sequence toestimation section 108 and coding section 101. Since different Walshsequences are associated with the same stream number in pattern A andpattern B, it is possible to reduce inter-sequence interference betweenterminals by assigning pattern A and pattern B to each terminal.

Furthermore, pilot information determining section 110 determines acyclic shift amount of each cyclic shift sequence capable of reducinginter-sequence interference between pilot signals in addition to thecorrespondence relationship. Pilot information determining section 110assigns a cyclic shift sequence having a large difference in the cyclicshift amount capable of reducing inter-sequence interference to eachstream. Pilot information determining section 110 then outputsinformation regarding the determined cyclic shift amount of the cyclicshift sequence to estimation section 108 and coding section 101.

On the other hand, DFT section 111 applies DFT processing to the datasignal inputted from separation section 105 and converts the data signalfrom a time-domain signal to a frequency-domain signal. DFT section 111outputs the data signal converted to the frequency-domain signal todemapping section 112.

Demapping section 112 extracts a data signal of a portion correspondingto the transmission band of each terminal from the signal inputted fromDFT section 111. Demapping section 112 then outputs the each extractedsignal to signal separation section 113.

Signal separation section 113 weights and combines the data signalsinputted from demapping section 112 according to transmissionpower/weight using the estimate value of the channel frequency responseinputted from estimation section 108 and thereby separates the datasignal into data signals of the respective streams. Signal separationsection 113 then outputs the data signals subjected to equalizationprocessing to IFFT (Inverse Fast Fourier Transform) section 114.

IFFT section 114 applies IFFT processing to the data signals inputtedfrom signal separation section 113. IFFT section 114 then outputs thesignal subjected to the IFFT processing to demodulation section 115.

Demodulation section 115 applies demodulation processing to the signalinputted from IFFT section 114 and outputs the signal subjected to thedemodulation processing to decoding section 116.

Decoding section 116 applies decoding processing to the signal inputtedfrom demodulation section 115 and outputs the signal subjected to thedecoding processing (decoded bit sequence) to error detection section117. Error detection section 117 performs error detection on the decodedbit sequence inputted from decoding section 116. For example, errordetection section 117 performs error detection using a CRC (CyclicRedundancy Check).

Error detection section 117 generates, when an error is detected in thedecoded bit as a result of error detection, a NACK signal as a responsesignal, and generates, when no error is detected in the decoded bit, anACK signal as a response signal. Error detection section 117 thenoutputs the response signal generated to coding section 101.Furthermore, when no error is detected in the decoded bit, errordetection section 117 outputs the data signal as the received data.

[Configuration of Terminal Station Apparatus]

FIG. 9 is a diagram illustrating terminal 200 according to the presentembodiment.

RF reception section 201 applies reception processing such asdown-conversion, A/D conversion to a signal from the base stationreceived via an antenna and outputs the signal subjected to thereception processing to demodulation section 202.

Demodulation section 202 applies equalization processing anddemodulation processing to the signal inputted from RF reception section201 and outputs the signal subjected to the processing to decodingsection 203.

Decoding section 203 applies decoding processing to the signal inputtedfrom demodulation section 202 and extracts received data and assignmentcontrol information from the signal subjected to the decodingprocessing. Here, the assignment control information includes a responsesignal (ACK signal/NACK signal), resource assignment information,control information, weight control information, information on cyclicshift amounts and information indicating a correspondence relationshipbetween a stream number and a Walsh sequence. Of the extractedassignment control information, decoding section 203 outputs theresource assignment information and control information to codingsection 207, modulation section 208 and assignment section 209 andoutputs the weight control information to transmission power/weightcontrol section 211 and outputs the information regarding the cyclicshift amounts and information indicating the correspondence relationshipbetween a stream number and a Walsh sequence to pilot informationdetermining section 204.

Pilot information determining section 204 stores a plurality ofcorrespondence relationships (patterns) between a stream number and aWalsh sequence and determines the correspondence relationship between astream number and a Walsh sequence, based on the information indicatingthe correspondence relationship between a stream number and a Walshsequence inputted from decoding section 203. The information indicatingthe correspondence relationship between a stream number and a Walshsequence is not limited to information reporting pattern A or pattern B,but may be information indicating whether the Walsh sequence used instream 0 is w1 or w2.

For example, when pattern A and pattern B as shown in FIG. 8 as thecorrespondence relationship between a stream number and a Walsh sequenceare stored, pilot information determining section 204 determines a Walshsequence used for each stream, based on information indicating thecorrespondence relationship (information on pattern A or pattern B)inputted from decoding section 203.

Furthermore, pilot information determining section 204 determines thecyclic shift amounts of the cyclic shift sequence according to theinformation on the cyclic shift amounts inputted from decoding section203. Pilot information determining section 204 then outputs thedetermined information to pilot signal generation section 205.

Pilot signal generation section 205 generates a pilot signal based onthe information on the cyclic shift amounts and Walsh sequences inputtedfrom pilot information determining section 204 and outputs the pilotsignal to multiplexing section 210. To be more specific, pilot signalgeneration section 205 spreads the cyclic shift sequence according tothe cyclic shift amount set by pilot information determining section 204using the Walsh sequence set by pilot information determining section204 and outputs the spread signal to multiplexing section 210.

CRC section 206 receives divided transmission data as input. CRC section206 performs CRC coding on the inputted transmission data to generateCRC coded data and outputs the generated CRC coded data to codingsection 207.

Coding section 207 codes the CRC coded data inputted from CRC section206 using the control information inputted from decoding section 203 andoutputs the coded data to modulation section 208.

Modulation section 208 modulates the coded data inputted from codingsection 207 using the control information inputted from decoding section203 and outputs the modulated data signal to assignment section 209.

Assignment section 209 assigns the data signal inputted from modulationsection 208 to frequency resources (RBs), based on the resourceassignment information inputted from decoding section 203. Assignmentsection 209 outputs the data signal assigned to RBs to multiplexingsection 210.

Multiplexing section 210 time-multiplexes the data signal and the pilotsignal inputted from assignment section 209 and outputs the multiplexedsignal to transmission power/weight control section 211.

Transmission power/weight control section 211 determines transmissionpower/weight based on the weight control information inputted fromdecoding section 203, multiplies each multiplexed signal inputted frommultiplexing section 210 by the transmission power/weight and outputsthe multiplexed signal after the multiplication to RF transmissionsection 212.

RF transmission section 212 applies transmission processing such as D/Aconversion, up-conversion, amplification to the multiplexed signalinputted from transmission power/weight control section 211 andtransmits by radio the signal after the transmission processing to thebase station from an antenna.

Next, the correspondence relationship between a stream number and aWalsh sequence will be described.

Here, in SU-MIMO, since one terminal transmits a plurality of streams,the same transmission bandwidths (bandwidths for transmitting datasignal) of the respective streams are set to the same value. This isbecause the amount of reporting control information of resourceassignment can be reduced by setting the same transmission bandwidth forone terminal. Thus, in SU-MIMO since the transmission bandwidth iscommon among sequences, it is possible to maintain orthogonality amongsequences through the cyclic shift sequences, provides a high effect ofreducing inter-sequence interference and produces less inter-sequenceinterference.

On the other hand, in MU-MIMO, a transmission bandwidth is reported toeach terminal, and each terminal can thereby set a differenttransmission bandwidth and set a transmission bandwidth adapted to achannel situation of each terminal. Therefore, when transmissionbandwidths are different among sequences, the cyclic shift sequencealone cannot maintain orthogonality among sequences, provides a lowereffect of inter-sequence interference and produces large inter-sequenceinterference.

Therefore, hereinafter the number of terminals in MU-MIMO is assumed tobe two in agreement with the number of terminals that can be generatedwith a Walsh sequence of a sequence length of 2 (length that can berealized in an LTE subframe configuration). Furthermore, a case will beassumed where each Walsh sequence is associated with two streams(=maximum number of streams/number of Walsh sequences under study inLTE-A) so that inter-sequence interference can be suppressed to a lowlevel from the standpoint including inter-sequence interference inSU-MIMO in addition to MU-MIMO. An appropriate correspondencerelationship between a stream number and a Walsh sequence in this casewill be studied.

In the present embodiment, terminals are configured to use mutuallyorthogonal Walsh sequences in MU-MIMO. The Walsh sequence can maintainorthogonality even when transmission bandwidths are different amongsequences.

FIG. 8 is a diagram illustrating an example of correspondence between astream number and a Walsh sequence. In MU-MIMO having two or fewerstreams to be assigned to each terminal, it is possible to use Walshsequences differing among terminals, and thereby maintain orthogonalityamong sequences. As described above, the stream number is a numberindicating the order in which data is assigned.

When the example of correspondence shown in FIG. 8 is used, in patternA, Walsh sequence w1 is set in a first stream group made up of a firststream (stream #0) and second stream (stream #1) and Walsh sequence w2is set in a second stream group made up of a third stream (stream #2)and fourth stream (stream #3). On the other hand, in pattern B, Walshsequence w2 is set in the first stream group and Walsh sequence w1 isset in the second stream group.

Here, as one method, each terminal determines a pattern based on controlinformation of pattern A or pattern B and in SU-MIMO, the first streamgroup and second stream group in the determined pattern are assigned tothe terminal. In MU-MIMO, the first stream group in the determinedpattern is assigned to the first terminal and the second stream group isassigned to the second terminal. Thus, mutually orthogonal Walshsequences are set in the first and second stream groups at least one ofwhich includes a plurality of streams and users are assigned in streamgroup units.

Furthermore, as another method, each terminal determines a pattern basedon control information of pattern A or pattern B, and when the number ofstreams used by the terminal for data transmission is equal to or fewerthan the number of streams included in the first stream group, eachterminal uses only the sequence assigned to the first stream group inthe determined pattern, whereas when the number of streams is greaterthan the number of streams included in the stream group, each terminaluses the sequences assigned to the first and second stream groups.

That is, when the correspondence relationship between a stream numberand a Walsh sequence as shown in FIG. 8 is used, pilot informationdetermining section 204 determines to use a Walsh sequence (w1 or w2)reported from the base station for the first stream, determines to usethe same Walsh sequence as the Walsh sequence of the first stream forthe second stream, and determines to use a Walsh sequence different fromthe first and second streams in the third and fourth streams.

As the number of streams increases, the separation performance generallydeteriorates a great deal, but in SU-MIMO, if the number of streams perterminal is 2 or less, streams can be separated using only cyclic shiftsequences while using the same Walsh sequence, and therefore performancedeterioration is small.

Thus, when mutually orthogonal Walsh sequences are set in the first andsecond stream groups, the first and second stream groups where mutuallyorthogonal Walsh sequences are assigned may be configured of two streamsalso for the following reasons.

As described above, in LTE-A uplink, as SU-MIMO, studies are beingcarried out on MIMO transmission with four antennas for transmission andreception respectively, that is, assuming that the maximum number ofstreams is four. Therefore, if the number of streams included in eachstream group is assumed to be 2, Walsh sequences w1 and w2 areassociated with two streams each.

Using two cyclic shift sequences corresponding to the maximum differencebetween the respective cyclic shift amounts in each stream group makesit possible to reduce inter-sequence interference that occurs betweenstreams. Therefore, when the maximum number of streams in MIMOtransmission is four, it is ensured that each stream group includes two(=maximum number of streams/Walsh sequences under study in LTE-A)streams. Thus, assigning different Walsh sequences to the respectivestream groups makes it possible to reduce inter-sequence interferenceoccurring between streams.

As a result, when SU-MIMO and MU-MIMO are simultaneously applied, it ispossible to reduce inter-sequence interference in pilot signals betweenterminals while suppressing inter-sequence interference in a pluralityof pilot signals used by the same terminal to a low level.

It is also assumed in MU-MIMO transmission that the first terminal usesthree streams and the second terminal uses one stream.

Thus, the number of streams N_(w) making up each stream group forassigning mutually orthogonal different Walsh sequences is sharedbetween the base station and terminal. Pilot information determiningsection 204 may also determine to use a Walsh sequence (w1 or w2)reported from the base station in the first to N_(w)-th streams and usea Walsh sequence different from the Walsh sequence reported by the basestation in the (N_(w)+1)-th and subsequent streams. In other words, oneterminal station may use one type of Walsh sequence (w1 or w2) in thefirst to N_(w)-th streams and use one type of Walsh sequence differentfrom the above-described Walsh sequence in the (N_(w)+1)-th andsubsequent streams. Whether the first stream is w1 or w2 may be directlyreported by the base station or indirectly reported as information ofpattern A or pattern B. For example, when two streams are assigned tothe terminal, N_(w)=2 may be shared between the base station andterminal, and when three streams are assigned to the terminal, N_(w)=3may be shared between the base station and terminal.

Thus, the correspondence relationship (pattern) between a stream numberand a Walsh sequence is changed according to N_(w) so as to use, forexample, the correspondence relationship in FIG. 8 when N_(w)=2, and usethe correspondence relationship in FIG. 10 when N_(w)=3. When the numberof streams is four and N_(w)=4 is assumed, the same Walsh sequence isused in all streams.

The N_(w) value corresponding to the number of streams of each terminalin MU-MIMO may be reported through signaling. At this time, in SU-MIMO,the same Walsh sequence as that of the first stream is used in the firstto N_(w)-th streams and a Walsh sequence different from the Walshsequence of the first stream is used in the (N_(w)+1)-th and subsequentstreams. This allows the number of streams using the same Walsh sequenceto be arbitrarily changed. Furthermore, the above-described techniqueand the conventional technique (FIG. 3) may be changed throughsignaling.

Also when the first terminal uses three streams and the second terminaluses one stream, mutually orthogonal Walsh sequences w1 and w2 are setfor the first stream group made up of three streams and for the secondstream group made up of one stream group. Assigning the first streamgroup to the first terminal and assigning the second stream group to thesecond terminal causes the first terminal and the second terminal to usedifferent Walsh sequences, which reduces inter-sequence interferencebetween terminals. Furthermore, assigning the first stream group ofpattern A to the first terminal and assigning the first stream group ofpattern B to the second terminal causes the first terminal and thesecond terminal to use different Walsh sequences, which reducesinter-sequence interference between terminals. Thus, when MU-MIMO wherethe number of streams of each terminal is three or more is assumed, itis possible to reduce inter-sequence interference between terminalsusing a Walsh sequence similar to that of the first stream also for theWalsh sequence used for the third stream.

Examples of the signaling method for changing N_(w) include (a) a methodof reporting per scheduling, and (b) a method of reporting at a longerinterval than scheduling (Higher Layer Signaling or the like).

Furthermore, N_(w) may be reported in a terminal-specific (UE Specific)manner or may be reported in a cell-specific (Cell Specific) manner.Furthermore, N_(w) may be reported implicitly according to the number ofthe cyclic shift amount. For example, when “0, 2, 3, 4, 6, 8, 9, 10”(that is, “0, 2, 3, 4, 6, 8, 9, 10”×symbol length/12(ms)) is defined asthe cyclic shift amount reported from the base station to the terminal,if any one of cyclic shift amounts “0, 2, 3, 4” is reported, N_(w)=2 isassumed and if any one of cyclic shifts “6, 8, 9, 10” is reported,N_(w)=4 is assumed.

For example, when N_(w)=2, mutually orthogonal Walsh sequences w1 and w2are set for the first stream group made up of two streams and for thesecond stream group made up of two stream groups. Furthermore, whenN_(w)=4, mutually orthogonal Walsh sequences w1 and w2 are set for thefirst stream group made up of four streams and for the second streamgroup made up of 0 stream groups. Then, N_(w) is changed explicitly orimplicitly. That is, the terminal transmits pilot signals of fourstreams using two types w1 and w2 when N_(w)=2 and transmits pilotsignals of four streams using any one of w1 and w2 when N_(w)=4. Inother words, Walsh sequences of the same sign are used for the firststream and second stream and Walsh sequences of the same sign as ordifferent sign from that of the first stream depending on the number ofstreams N_(w) making up each stream group in the third and subsequentstreams.

Thus, the N_(w) value can be changed through signaling, and it isthereby possible to use the number of streams N_(w) set according to theseparation performance of spatially multiplexed signals in MU-MIMO andflexibly reduce inter-sequence interference.

In the above description, a Walsh sequence is associated with a streamnumber, but a cyclic shift amount can also be associated with a streamnumber in addition to a Walsh sequence. For example, as shown in FIG.11, cyclic shift sequences (here, suppose “0, 1, 2, 3, 4, 5, 6, 7, 8, 9,10, 11” (that is, “0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11”×symbollength/12(ms)) are selectable as the cyclic shift amounts) having alarge difference in cyclic shift amounts is assigned to the same Walshsequence.

To be more specific, when cyclic shift amount Δ0 (Δ0<12) used for thefirst stream (stream #0) is reported from the base station, cyclic shiftamount Δ1 used for the second stream (stream #1) is assumed to be(Δ0+6)mod 12 and the cyclic shift amount is assumed to be a ½ symbollength (see pattern 1 and pattern 2 in FIG. 11). Furthermore, supposecyclic shift amount Δ2 used for the third stream (stream #2) is(Δ0+3)mod 12, the cyclic shift amount is a ¼ symbol length, cyclic shiftamount Δ3 used for the fourth stream (stream #3) is (Δ0+9)mod 12 and thecyclic shift amount is a ¾ symbol length (see pattern 1 in FIG. 11).Cyclic shift amount Δ2 used for the third stream (stream #2) may be(Δ0+9)mod 12 and cyclic shift amount Δ3 used for the fourth stream(stream #3) may be (Δ0+3)mod 12 (see pattern 2 in FIG. 11).

This allows the difference in the cyclic shift amount to be a ½ symbollength not only between sequences using Walsh sequence w1 but alsobetween sequences using Walsh sequence w2 and also allows the differencein the cyclic shift amount to be largest, and thereby allowsinter-sequence interference to be drastically reduced. On the otherhand, the difference in the cyclic shift amount is set to a ¼ symbollength between different Walsh sequences (w1 and w2) to thereby reduceinter-sequence interference in cyclic shift sequences and further reduceinter-sequence interference in different Walsh sequences.

Thus, when the sum of the number of streams per terminal in SU-MIMO andthe number of streams of the terminals in MU-MIMO (hereinafter referredto as “number of operating streams”) is four, inter-sequenceinterference can be drastically reduced using “0, 6, 3, 9” (or “0, 6, 9,3”) as the amount of offset of the cyclic shift amount for the first tofourth streams.

When the number of operating streams is three, “0, 6, 3” or “0, 4, 8”may be used as the amount of offset of the cyclic shift amount for thefirst to third streams. Here, the amount of offset “0, 6, 3” ispartially common to the amount of offset “0, 6, 3, 9” applicable to thecase where the number of operating streams is four. Therefore, when thenumber of operating streams is three, it is possible to use part of theprocessing in the case where the number of operating streams is four byusing “0, 6, 3” as the amount of offset of the cyclic shift amount. Thatis, since the same circuit can be used in the cases where the number ofoperating streams is three and four, the circuit scale can be reduced.However, when “0, 6, 3” is used as the amount of offset of the cyclicshift amount, the interval of cyclic shift amounts between streams isthree. On the other hand, when the number of operating streams is three,if “0, 4, 8” is used as the amount of offset of the cyclic shift amount,the interval of cyclic shift amounts between streams is four and theinterval of cyclic shift amounts can be widened to a maximum degree.Therefore, when the number of operating streams is three, using “0, 4,8” as the amount of offset of the cyclic shift amount has a greatereffect of reducing inter-sequence interference than using “0, 6, 3.”

As described above, pilot information determining section 204 determinesrespective Walsh sequences of the first and second stream groups, atleast one of which includes a plurality of streams, based on assignmentcontrol information and pilot signal generation section 205 spreads eachstream included in the first and second stream groups with thedetermined Walsh sequence and thereby forms a transmission signal. Atthis time, mutually orthogonal Walsh sequences are set in the first andsecond stream groups and users are assigned in stream group units.

Modification Example 1

A case has been described above where in MU-MIMO transmission, Walshsequence w1 is assigned to the first stream group made up of first tothird streams and Walsh sequence w2 is assigned to the second streamgroup made up of only the fourth stream as an example of N_(w)=3.

In this case, in SU-MIMO, the same Walsh sequence w1 is assigned to thefirst to third streams included in the first stream group, and it istherefore necessary to reduce interference between three sequences usingcyclic shift sequences. However, even when N_(w)=3, since the differencein the cyclic shift amount between cyclic shift sequences issufficiently large, inter-sequence interference can be sufficientlyreduced.

Thus, in SU-MIMO, even when the same transmission bandwidth is usedbetween sequences, the difference in the cyclic shift amount betweencyclic shift sequences decreases as the number of streams increases andinter-sequence interference between cyclic shift sequences increases.That is, in SU-MIMO, when the number of streams making up a stream groupis small, the difference in the cyclic shift amount can be increased andtherefore even when the same Walsh sequence is used, inter-sequenceinterference can be sufficiently reduced only with cyclic shiftsequences, whereas when the number of streams making up the stream groupis large, the difference in the cyclic shift amount decreases andinter-sequence interference between sequences increases.

Thus, in SU-MIMO, when the number of streams of a stream group is small,Walsh sequences of the same sign are applied and when the number ofstreams of the stream group is large, Walsh sequences of the same signor a different sign may also be applied. To be more specific, inSU-MIMO, Walsh sequence w1 or w2 is applied when the number of streamsof a stream group is two or fewer, whereas when the number of streams ofa stream group is three or more, Walsh sequences w1 and w2 are applied.When the number of streams per terminal is three or more, the firststream group to which Walsh sequence w1 is assigned and the secondstream group to which Walsh sequence w2 is assigned are assigned to asingle user. That is, in this case, the first and second stream groupsfor which mutually orthogonal Walsh sequences are set are assigned to asingle user.

A case has been described above where the number of streams is four orfewer as an example, but it may also be assumed that the correspondencerelationship in the first and subsequent streams is repeated in thefifth and subsequent streams. That is, a Walsh sequence of w1 may beused in the first and fifth streams, the second and sixth streams.

The base station and terminal according to the present invention mayalso be replaced by the following.

The base station includes pilot information determining section 110 as asetting section that classifies a stream defined in one terminal into afirst stream group and a second stream group, and selects and sets asequence used in the first stream group and the second stream group froma first Walsh sequence or second Walsh sequence for each terminal, pilotinformation determining section 110 as a control information generationsection that generates control information indicating whether thesequence used in the set first stream group is the first Walsh sequenceor the second Walsh sequence, and RF transmission section 103 as atransmission section that transmits the control information, whereinpilot information determining section 110 as the setting section assignsdifferent Walsh sequences to the first stream group and the secondstream group in each terminal.

The terminal includes RF reception section 201 as a reception sectionthat classifies a stream defined in one terminal into a first streamgroup and a second stream group, and receives control informationindicating whether a sequence used in the first stream group is a firstWalsh sequence or a second Walsh sequence, demodulation section 202 anddecoding section 203, pilot information determining section 204 as asetting section that assigns a sequence reported by the controlinformation to the first stream group and assigns a sequence differentfrom the sequence reported by the control information to the secondstream group based on the control information, pilot signal generationsection 205 as a formation section that forms a transmission signalusing the set Walsh sequence and RF transmission section 212 as atransmission section that transmits the formed transmission signal,where pilot signal generation section 205 as the formation section: usesonly the sequence assigned to the first stream group when the number ofstreams used by the terminal for data transmission is equal to or fewerthan the number of streams included in the first stream group; and usesthe sequence assigned to the first and second stream groups, when thenumber of streams is greater than the number of streams included in thestream group.

Embodiment 2

Embodiment 1 assumes that information on the correspondence relationshipbetween a stream number and a Walsh sequence and information on thecyclic shift sequences are reported per scheduling. To be more specific,in LTE, the base station selects a cyclic shift amount of each cyclicshift sequence from among eight types (cyclic shift amounts defined inLTE) and reports the selected cyclic shift amount to the terminal usingthree bits. Furthermore, in LTE-A, studies are being carried out on abase station selecting any one of w1 and w2 as a Walsh sequence andreporting the selected sequence to the terminal using one bit.

Therefore, according to Embodiment 1, the terminal selects a cyclicshift sequence and a Walsh sequence from among 16 types of combinations;eight types of cyclic shift sequences and two types of Walsh sequences.However, in a real environment of LTE-A uplink, the number of streamsassumed as the number of streams used in SU-MIMO or MU-MIMO is four atmost and it is sufficient that four sequences having littleinter-sequence interference be able to be selected as pilot signals.With all these aspects taken into consideration, there are manyalternatives (16 types) in selecting a pilot signal sequence withrespect to the number of sequences to be code-multiplexed (four types atmost).

That is, in consideration of the necessity for providing only foursequences as sequences with less inter-sequence interference, influencesof pilot signals on inter-sequence interference are small even whenalternatives (degree of freedom) of pilot signals are reduced. In otherwords, it may be considered unnecessary such flexibility (degree offreedom) that both cyclic shift sequences and Walsh sequences arereported to each terminal per scheduling.

On the other hand, in MU-MIMO, terminals to be spatially multiplexeddiffer from one scheduling instance to another. Therefore, it ispreferable that in MU-MIMO, different Walsh sequences be able to set perscheduling and spatial multiplexing be able to be performed betweendifferent terminals per scheduling. In other words, it is preferablethat Walsh sequences be able to be adjusted with information reportedfrom the base station per scheduling.

Thus, the present embodiment associates a Walsh sequence with a cyclicshift amount of each cyclic shift sequence used for a first stream andchanges a correspondence relationship (pattern) indicating a pair of thecyclic shift amount and Walsh sequence at an interval longer than thatof scheduling. That is, the base station reports a cyclic shift amountper scheduling and reports a correspondence relationship (pattern)indicating a pair of a cyclic shift amount and a Walsh sequence at aninterval longer than that of scheduling. This causes a reception cycleof a correspondence relationship (pattern) indicating a pair of a cyclicshift amount and a Walsh sequence in the terminal to be longer than areception cycle of a cyclic shift amount, and can thereby suppressincreases in the amount of reporting of Walsh sequences. Furthermore,since the terminal can set Walsh sequence w1 or w2 according toinformation on the cyclic shift amount reported from the base stationper scheduling, it is possible to suppress increases in the amount ofreporting of Walsh sequences while maintaining the degree of freedomwithin which Walsh sequences can be changed per scheduling.

The above-described correspondence relationship may be reported in amanner that differs from one cell to another (cell-specific) or may bereported in a manner that differs from one terminal to another (userspecific). In the case of cell-specific reporting, only informationcommon to respective terminals in the cell needs to be reported, and itis thereby possible to reduce the amount of reporting. On the otherhand, in the case of user-specific reporting, since association ofcyclic shift sequences and Walsh sequences can be set for each terminal,flexibility of sequences assigned to each terminal increases. Forexample, when a correspondence relationship in which w1 is associatedwith a cyclic shift sequence of cyclic shift amount 2 is used for thefirst terminal, and a correspondence relationship in which w2 isassociated with a cyclic shift sequence of cyclic shift amount sequence2 is used for the second terminal, it may be possible to assign cyclicshift sequence 2 to the first and second terminals and perform codemultiplexing using Walsh sequences w1 and w2. Furthermore, in this case,it is also possible to reduce the amount of reporting used to reportWalsh sequences compared to the prior art that reports Walsh sequencesto each terminal.

The configuration of the base station according to Embodiment 2 of thepresent invention is similar to the configuration of Embodiment 1 shownin FIG. 7 and is different only in some functions, and therefore onlydifferent functions will be described using FIG. 7.

Pilot information determining section 110 stores an operating sequenceidentification table storing a plurality of candidates for pairs of acyclic shift amount and a Walsh sequence.

FIG. 12 is a diagram illustrating an example of the operating sequenceidentification table according to the present embodiment. The operatingsequence identification table defines a correspondence relationship(pattern) between two patterns; pattern 1 and pattern 2, as candidatesfor pairs of a cyclic shift amount of each cyclic shift sequence and aWalsh sequence used for a first stream.

In pattern 1, Walsh sequences “w2, w2, w2, w2, w1, w1, w1, w1” areassociated with cyclic shift amounts “0, 2, 3, 4, 6, 8, 9, 10.” On theother hand, in pattern 2, Walsh sequences “w1, w1, w1, w1, w2, w2, w2,w2” are associated with cyclic shift amounts “0, 2, 3, 4, 6, 8, 9, 10.”

Thus, when attention is focused, for example, on the cyclic shiftsequence of cyclic shift amount 0, the operating sequence identificationtable defines a pair of cyclic shift amount 0 and Walsh sequence w1 anda pair of cyclic shift amount 0 and Walsh sequence w2 according topattern 1 or pattern 2.

Pilot information determining section 110 determines transmission bandsof pilot signals based on the resource assignment information inputtedfrom scheduling section 109, and selects the above-describedcorrespondence relationship (pattern) that can reduce inter-sequenceinterference of these pilot signals.

Pilot information determining section 110 outputs information indicatingthe selected correspondence relationship (pattern) to coding section 101and estimation section 108. When the operating sequence identificationtable is configured of only one pattern, it is not necessary to reportwhich pattern is selected or report the selected pattern, and it istherefore unnecessary to report information indicating the selectedcorrespondence relationship (pattern).

Furthermore, pilot information determining section 110 determines acombination (pair) of a cyclic shift sequence and a Walsh sequence ofthe first stream from the selected correspondence relationship(pattern).

Pilot information determining section 110 determines Walsh sequences ofpilot signals used in the second and subsequent streams in substantiallythe same way as in Embodiment 1. That is, pilot information determiningsection 110 determines correspondence relationships with Walsh sequencesin the second and subsequent streams from among correspondencerelationships between a stream number and a Walsh sequence (e.g.,pattern A and pattern B shown in FIG. 8) based on the Walsh sequences ofthe first stream determined above. For example, pilot informationdetermining section 110 determines pattern A when the Walsh sequence ofthe first stream is w1 and determines pattern B when w2.

Furthermore, pilot information determining section 110 determines cyclicshift amounts of cyclic shift sequences in the second and subsequentstreams in addition to the correspondence relationship. For example,pilot information determining section 110 determines cyclic shiftamounts of cyclic shift sequences in the second and subsequent streamsby adding a fixed offset to the cyclic shift amount of the first stream.Alternatively, assuming the cyclic shift amounts of cyclic shiftsequences in the second and subsequent streams are reported as controlinformation, pilot information determining section 110 may determine thecyclic shift amounts of cyclic shift sequences in the second andsubsequent streams based on this control information. Pilot informationdetermining section 110 then outputs information indicating thedetermined cyclic shift amounts and information indicating thecorrespondence relationship between a stream number and a Walsh sequenceto estimation section 108 and outputs information indicating the cyclicshift amount to coding section 101.

The base station then reports the cyclic shift amounts used for cyclicshift sequences in the first stream per scheduling.

Furthermore, the base station reports information indicating whichcorrespondence relationship of pattern 1 or pattern 2 is used to theterminal at an interval longer than a scheduling interval. Examples ofsignaling reported at an interval longer than a scheduling intervalinclude MAC header, RRC signaling or higher layer signaling such asbroadcast information.

The configuration of the terminal according to Embodiment 2 of thepresent invention is similar to the configuration of Embodiment 1 shownin FIG. 9 and is different only in some functions, and therefore onlydifferent functions will be described using FIG. 9.

Pilot information determining section 204 stores an operating sequenceidentification table storing a plurality of correspondence relationships(patterns) between a cyclic shift amount and a Walsh sequence. Pilotinformation determining section 204 then determines the correspondencerelationship between a cyclic shift amount and a Walsh sequence, basedon information indicating the correspondence relationship between acyclic shift amount and a Walsh sequence inputted from decoding section203 (information reported at an interval longer than that ofscheduling).

For example, as the correspondence relationship between a cyclic shiftamount and a Walsh sequence, the operating sequence identification tablestores pattern 1 and pattern 2 as shown in FIG. 12, and pilotinformation determining section 204 determines the correspondencerelationship based on the information indicating the correspondencerelationship between a cyclic shift amount and a Walsh sequence inputtedfrom decoding section 203 (information on pattern 1 or pattern 2).

Furthermore, pilot information determining section 204 determines aWalsh sequence according to information on the cyclic shift amountinputted from decoding section 203 and the above-describedcorrespondence relationship. The information determined here isoutputted to pilot signal generation section 205.

Pilot information determining section 204 determines pilot signals usedin the second and subsequent streams in substantially the same way as inpilot information determining section 110. For example, pilotinformation determining section 204 stores a plurality of correspondencerelationships between a stream number and a Walsh sequence, anddetermines the correspondence relationships with Walsh sequences in thesecond and subsequent streams from among correspondence relationshipsbetween a stream number and a Walsh sequence (e.g., pattern A or patternB shown in FIG. 8), based on the determined Walsh sequence (w1 or w2) ofthe first stream.

Furthermore, pilot information determining section 204 determines cyclicshift amounts of cyclic shift sequences in the second and subsequentstreams according to information on the cyclic shift amount of the firststream inputted from decoding section 203 in the same way as in pilotinformation determining section 110. The cyclic shift amounts of thecyclic shift sequences determined here are outputted to pilot signalgeneration section 205.

Next, the correspondence relationship (pattern) between a cyclic shiftamount and a Walsh sequence according to the present embodiment will bedescribed in detail. In the present embodiment, pilot informationdetermining section 204 stores an operating sequence identificationtable storing a plurality of correspondence relationships (patterns)between a cyclic shift amount and a Walsh sequence, and switches betweenthe correspondence relationships (patterns) at an interval longer thanthe scheduling interval.

The present embodiment reports information indicating a correspondencerelationship (pattern) between a cyclic shift amount and a Walshsequence at an interval longer than the scheduling interval, and canthereby suppress increases in the amount of reporting. Furthermore, byassociating a cyclic shift amount with a Walsh sequence, it is possibleto change a Walsh sequence by selecting a cyclic shift amount, andthereby maintain the degree of freedom in changing a Walsh sequence perscheduling.

That is, the cyclic shift amount of a cyclic shift sequence isinformation reported per scheduling, and by associating the cyclic shiftamount of a cyclic shift sequence with a Walsh sequence, it is possibleto control the cyclic shift amount of a cyclic shift sequence reportedper scheduling and set a Walsh sequence, and thereby change a Walshsequence per scheduling.

Furthermore, by defining a plurality of correspondence relationships(patterns) between a cyclic shift amount and a Walsh sequence andselecting one of the plurality of correspondence relationships(patterns), the possibility that both w1 and w2 may be associated asWalsh sequences associated with their respective cyclic shift amountsincreases and the flexibility of Walsh sequences assigned to eachterminal can be increased. For example, in two types of patterns in FIG.12, w1 and w2 are associated with a cyclic shift sequence of a cyclicshift amount of 2, and therefore when the cyclic shift sequence ofcyclic shift amount 2 is assigned to the terminal, selection is possiblefrom two types of Walsh sequences w1 and w2.

Furthermore, when eight types of cyclic shift amounts and two types ofWalsh sequences are used to a maximum degree for the number ofcode-multiplexed sequences (four types at most), there are as many as 16alternatives in selecting a sequence of pilot signals, and thereforeeven when the number of alternatives (degree of freedom) of pilotsignals is reduced, influences of the pilot signals on inter-sequenceinterference are small. Therefore, even when the number of alternativesdecreases (flexibility deteriorates) in the cyclic shift sequence andWalsh sequence, influences on the performance of the entire system aresmall.

A case has been described above where a plurality of correspondencerelationships (patterns) between a cyclic shift amount and a Walshsequence are provided and the correspondence relationships (patterns)are reported at a long interval, but the correspondence relationships(patterns) may be fixed to one type as shown in FIG. 13. This results inreporting with only three bits of a cyclic shift amount as in the caseof the prior art, and can thereby further reduce the amount of reportingon Walsh sequences. Furthermore, as described above, when eight types ofcyclic shift amounts and two types of Walsh sequences are used to amaximum degree with respect to the number of code-multiplexed sequences(four types at most), there are as many as 16 alternatives in selectinga sequence of pilot signals, and therefore even when the number ofalternatives (degree of freedom) of pilot signals is reduced, influencesof the pilot signals on inter-sequence interference are small.

When only an LTE-A terminal is assumed, associating the same number ofWalsh sequences w1 and w2 with cyclic shift sequences makes it possibleto equalize the probabilities of w1 and w2 being used respectively andsubstantially equalize the probabilities of inter-sequence interferenceoccurring between pilot signals. Of the pairs of a cyclic shift amountand a Walsh sequence, the patterns shown in FIG. 12 and FIG. 13respectively are examples where the number of pairs with Walsh sequencew1 and the number of pairs with Walsh sequence w2 are equal. That is, inthe respective patterns shown in FIG. 12 and FIG. 13, four Walshsequences w1 and four Walsh sequences w2 are associated with eight typesof cyclic shift amounts. Here, when “0, 2, 3, 4, 6, 8, 9, 10” aredefined as cyclic shift amounts as in LTE, a correspondence relationshipbetween cyclic shift amounts “0, 2, 3, 4, 6, 8, 9, 10” and Walshsequences may be defined. Furthermore, when other “1, 5, 7, 11” aredefined as cyclic shift amounts, a correspondence relationship betweenall cyclic shift amounts “0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11” andWalsh sequences may be defined.

Furthermore, when cyclic shift amount Δ0 (Δ0<12) used for the firststream is reported, cyclic shift amount Δ1 used for the second stream isassumed to be (Δ0+6)mod 12, and the cyclic shift amount is assumed to bea ½ symbol length so that the interval between cyclic shift amountsbecomes largest (difference in cyclic shift amounts becomes a maximum)(that is, the interval between cyclic shift amounts is 6), with respectto the pair of the cyclic shift amounts, which are most distant fromeach other (e.g., cyclic shift amount (0, 6)), the Walsh sequenceassociated with one cyclic shift amount that forms the pair may bedifferent from the Walsh sequence associated with the other cyclic shiftamount.

FIG. 14 is an example of the operating sequence identification table inwhich of a pair of cyclic shift amounts, which are most distant fromeach other (e.g., cyclic shift amount (0, 6)), the Walsh sequenceassociated with the one cyclic shift amount that forms the pair isdifferent from the Walsh sequence associated with the other cyclic shiftamount. As shown in FIG. 14, for example, Walsh sequence w1 isassociated with cyclic shift amount “0” and w2 is associated with cyclicshift amount “6” which is most distant from the cyclic shift amount “6”.Similarly, Walsh sequence w1 is associated with cyclic shift amounts “2,3, 4” and w2 is associated with cyclic shift amounts “8, 9, 10” whichare most distant from cyclic shift amounts “2, 3, 4” respectively. Thus,as shown in FIG. 14, different Walsh sequences w1 and w2 are associatedwith cyclic shift amounts making up pairs of cyclic shift amounts (0,6), (2, 8), (3, 9), (4, 10), which are most distant from each otherrespectively.

As shown in the operating sequence identification table in FIG. 14,advantages in the case where cyclic shift amount Δ1 of the second streamis set to a cyclic shift amount (that is, Δ1=Δ0+6), which is mostdistant from cyclic shift amount Δ0 of the first stream, will bedescribed using FIG. 15.

In FIG. 15, candidates for pairs of a cyclic shift amount of each cyclicshift sequence and a Walsh sequence used for the first stream aredefined in an operating sequence identification table. A case will thenbe considered where cyclic shift amount Δ1 of the second stream is setto a cyclic shift amount (that is, Δ1=Δ0+6) most distant from cyclicshift amount Δ0 of the first stream. At this time, when “0” is reportedas cyclic shift amount Δ0 of the first stream, cyclic shift amount Δ1 ofthe second stream is set to “6” and Walsh sequences of the first andsecond streams are set to w1. On the other hand, when “6” is reported ascyclic shift amount Δ0 of the first stream, cyclic shift amount Δ1 ofthe second stream is set to “0” and Walsh sequences of the first andsecond streams are set to w2.

That is, both the pairs of cyclic shift amounts of the first and secondstreams are (0,6), but Walsh sequences set in the first and secondstreams can be switched depending on which of “0” or “6” the basestation reports to the terminal as cyclic shift amount Δ0 of the firststream.

Thus, when the cyclic shift amount of the second stream is set to acyclic shift amount distant by a predetermined amount of offset from thecyclic shift amount of the first stream in the operating sequenceidentification table, different Walsh sequences are associated with thecyclic shift amounts (CS1 and CS2) distant from each other by thepredetermined amount of offset. Thus, it is possible to set differentWalsh sequences in the first and second streams depending on whether thecyclic shift amount reported from the base station to the terminal isCS1 or CS2.

On the other hand, when the cyclic shift amount of the second stream isset to a cyclic shift amount most distant from the cyclic shift amountof the first stream, if the same Walsh sequence is associated with thecyclic shift amounts (CS1 and CS2), which are most distant from eachother in the cyclic shift amount, the same Walsh sequence is setregardless of whether the cyclic shift amount reported from the basestation to the terminal is CS1 or CS2. For this reason, the degree offreedom in changing Walsh sequences is reduced compared to a case wheredifferent Walsh sequences are associated with the cyclic shift amounts(CS1 and CS2), which are most distant from each other. Furthermore, inorder to switch between Walsh sequences associated with cyclic shiftamounts (CS1 and CS2) which are most distant from each other, asdescribed using FIG. 12, it is necessary to report through higher layersignaling which pattern should be used, which requires an extrareporting bit.

Modification Example 1

While LTE-A terminals use Walsh sequence w1 or w2, LTE terminals are notassumed to use Walsh sequences and have no requirements regarding Walshsequences, which is equivalent to always using Walsh sequence w1. Here,assuming an environment in which LTE terminals and LTE-A terminalscoexist, while the probabilities of LTE-A terminals using Walsh sequencew1 and w2 are substantially the same, the probability of LTE terminalsusing Walsh sequence w1 is higher. Therefore, when Walsh sequence w1 isused, the probability of inter-sequence interference occurring in pilotsignals is higher than when Walsh sequence w2 is used.

Thus, among pairs of a cyclic shift sequence and a Walsh sequence in acorrespondence relationship (pattern) stored in the operating sequenceidentification table, the number of pairs of Walsh sequence w1 is madeto be smaller than the number of pairs of Walsh sequence w2. Here, Walshsequence w1 is [1 1] and is a sequence, all elements of which arecomposed of “1” s.

FIG. 16 is a diagram illustrating candidates for pairs of a cyclic shiftsequence and a Walsh sequence. As shown in FIG. 16, for example, Walshsequences “w1, w1, w1, w2, w2, w2, w2, w2” are associated with cyclicshift amounts “0, 2, 3, 4, 6, 8, 9, 10” respectively, and suppose thenumber of pairs with Walsh sequence w1 is three and the number of pairswith Walsh sequence w2 is five so that the number of pairs with Walshsequence w1 is smaller than the number of pairs with Walsh sequence w2.

Thus, providing a difference between the number of pairs with Walshsequence w1 and the number of pairs with Walsh sequence w2 causes Walshsequence w2 less prone to inter-sequence interference to be more likelyto be selected than Walsh sequence w1 used by LTE terminals, and canthereby reduce inter-sequence interference from LTE terminals.

For example, in an environment in which there are many LTE terminals,making it easier to use Walsh sequences of w2 in pattern 2 can reduceinter-sequence interference in pilot signals, while in an environment inwhich the number of LTE terminals is at the same level as that of LTE-Aterminals, inter-sequence interference in pilot signals can be reducedby using substantially the same number of Walsh sequences w1 and w2 inpattern 1. This correspondence relationship is changed at an intervallonger than that of scheduling.

Modification Example 2

In a cyclic shift sequence, the smaller the distance in cyclic shiftamounts between cyclic shift sequences, the greater is inter-sequenceinterference. Inter-sequence interference is large, for example, betweena cyclic shift sequence having a cyclic shift amount of 2 and a cyclicshift sequence having a cyclic shift amount of 1 or 3. Therefore, thecloser in cyclic shift amounts, the more preferable it is to reduceinter-sequence interference using different Walsh sequences.

Thus, when neighboring cyclic shift amounts are discontinuous, any oneof the same Walsh sequence and a different Walsh sequence is associatedand when neighboring cyclic shift amounts are continuous, Walshsequences of different signs are associated.

FIG. 17 is a diagram illustrating candidates for pairs of a cyclic shiftsequence and a Walsh sequence. As shown in FIG. 17, Walsh sequences “w2,w1, w2, w1, w2, w2, w1, w2” are associated with cyclic shift amounts “0,2, 3, 4, 6, 8, 9, 10” respectively and different Walsh sequences amongneighboring cyclic shift amounts are associated with continuous cyclicshift amounts “2, 3, 4” and “8, 9, 10.”

Thus, by making Walsh sequences that form pairs with neighboring cyclicshift amounts differ from each other, it is possible to reduceinter-sequence interference between cyclic shift sequences ofneighboring cyclic shift amounts having maximum inter-sequenceinterference.

(Modification example 1) and (modification example 2) may be combined.For example, in FIG. 17, the number of pairs with Walsh sequence w1 isthree and the number of pairs with Walsh sequence w2 is five so that thenumber of pairs with Walsh sequence w1 is smaller than the number ofpairs with Walsh sequence w2.

Modification Example 3

In a cyclic shift sequence, the smaller the distance in cyclic shiftamounts between cyclic shift sequences, the greater is inter-sequenceinterference. Therefore, the smaller the distance in cyclic shiftamounts between cyclic shift sequences, the more preferable it is to usedifferent Walsh sequences.

Therefore, Walsh sequence w2 is paired with cyclic shift sequences ofodd-numbered cyclic shift amounts and Walsh sequence w1 is paired withcyclic shift sequences of even-numbered cyclic shift amounts.

FIG. 18 and FIG. 19 are diagrams illustrating candidates for pairs of acyclic shift sequence and a Walsh sequence. As shown in FIG. 19, alsowhen the number of operating streams is assumed to be four, differentWalsh sequences can be set between neighboring cyclic shift amounts, andtherefore inter-sequence interference can be reduced. For example, thefirst terminal may use cyclic shift amounts “0, 6” and the secondterminal may use cyclic shift amounts “3, 9” to perform MU (MultiUser)-MIMO, and can thereby set different Walsh sequences amongneighboring cyclic shift amounts while keeping the maximum intervalbetween cyclic shift amount, and thereby reduce inter-sequenceinterference.

Furthermore, in LTE-A uplink MIMO transmission, not only cyclic shiftamounts reported in LTE but all cyclic shift amounts may be used. Forexample, when cyclic shift amounts of the second stream are determinedwith an offset from the first stream, if offset amount 3 and cyclicshift amount 2 of the first stream are reported, the cyclic shift amountof the second stream is determined to be 5, and cyclic shift amount 5which is not defined in LTE is used. In this case, if theabove-described correspondence relationship is used, different Walshsequences between neighboring cyclic shift amounts are also used, and itis thereby possible to reduce inter-sequence interference between cyclicshift sequences whose cyclic shift amounts are close to each other.

In the second and subsequent streams, Walsh sequences may be set as inthe case of Embodiment 1 or without being limited to this, Walshsequences may also be set in the second and subsequent streams as in thecase of the first stream. For example, the base station may reportcyclic shift amounts in the second and subsequent streams so that codesof Walsh sequences may be derived from cyclic shift amounts as in thecase of the above-described first stream. Even if Embodiment 2 isapplied independently of Embodiment 1, it is possible to suppressincreases in the amount of reporting Walsh sequences.

Embodiment 3

In Embodiment 2, the correspondence relationship between a cyclic shiftamount and a Walsh sequence used for the first stream is defined in theoperating sequence identification table. Then, a case has been describedwhere Walsh sequences of the second stream are Walsh sequences havingthe same sign as that in the first stream, Walsh sequences in the thirdand subsequent streams are selected from among Walsh sequences havingthe same sign as or a sign different from that of Walsh sequences usedin the first and second streams or Walsh sequences having a signdifferent from that of the Walsh sequences in the first and secondstreams. That is, a method of implicitly determining Walsh sequences inthe second and subsequent streams from stream numbers has beendescribed.

The present embodiment will describe a method of implicitly determiningWalsh sequences in the first stream, and second and subsequent streamsaccording to cyclic shift amounts using one operating sequenceidentification table indicating a correspondence relationship between acyclic shift amount and a Walsh sequence. That is, the presentembodiment implicitly determines Walsh sequences in the first to fourthstreams according to cyclic shift amounts using an operating sequenceidentification table independent of the number of streams (rank).

In the present embodiment, the base station and terminal share offsetinformation, which is a difference between a cyclic shift amount of thefirst stream and cyclic shift amounts in the second to fourth streamsbeforehand, and the base station and terminal determines a cyclic shiftamount of each stream based on the offset information.

FIG. 20 is a diagram illustrating an example of offset informationindicating a difference between the cyclic shift amount of the firststream and the cyclic shift amounts of the second to fourth streams.Based on the offset information shown in FIG. 20, upon receiving areport from the base station on cyclic shift amount Δ0 (Δ0<12) used forthe first stream (stream #0), the terminal assumes cyclic shift amountΔ1 used for the second stream (stream #1) to be (Δ0+6)mod 12, cyclicshift amount Δ2 used for the third stream (stream #2) to be (Δ0+3)mod12, and cyclic shift amount Δ3 used for the fourth stream (stream #3) tobe (Δ0+9)mod 12 (pattern 1 in FIG. 20). Alternatively, the terminalassumes cyclic shift amount Δ2 used for the third stream (stream #2) tobe (Δ0+9)mod 12, and cyclic shift amount Δ3 used for the fourth stream(stream #3) to be (Δ0+3)mod 12 (pattern 2 in FIG. 20).

Since the configuration of the base station according to Embodiment 3 ofthe present invention is similar to the configuration of Embodiment 1shown in FIG. 7 and is different only in some functions, only differentfunctions will be described using FIG. 7.

Pilot information determining section 110 determines cyclic shiftamounts in cyclic shift sequences used for the second to fourth streams.Here, the cyclic shift amounts in the second and subsequent streams aredetermined by adding a fixed offset to the cyclic shift amount of thefirst stream. For example, when the base station and terminal share theoffset information shown in pattern 1 in FIG. 20, if the cyclic shiftamount used for the first stream (stream #0) from the base station isassumed to be 40 (Δ0<12), pilot information determining section 110determines cyclic shift amount Δ1 used for the second stream (stream #1)to be (Δ0+6)mod 12, determines cyclic shift amount Δ2 used for the thirdstream (stream #2) to be (Δ0+3)mod 12 and determines cyclic shift amountΔ3 used for the fourth stream (stream #3) to be (Δ0+9)mod 12.

Furthermore, pilot information determining section 110 stores anoperating sequence identification table storing a plurality ofcandidates for pairs of a cyclic shift amount and a Walsh sequence.

FIG. 21 is a diagram illustrating an example of the operating sequenceidentification table according to the present embodiment. The operatingsequence identification table defines candidates for pairs of a cyclicshift amount of each cyclic shift sequence and a Walsh sequence used forthe first stream. To be more specific, Walsh sequences “w1, (w1), w2,w2, w1, (w2), w1, (w1), w2, w2, w1, (w2)” are associated with cyclicshift amounts “0, (1), 2, 3, 4, (5), 6, (7), 8, 9, 10, (11).”

Pilot information determining section 110 then sets Walsh sequencescorresponding to the reported cyclic shift amounts of the first streamin Walsh sequences of the first stream based on the operating sequenceidentification table. Furthermore, Walsh sequences corresponding tocyclic shift amounts Δ1, Δ2 and Δ3 of the second, third and fourthstreams are determined respectively.

Pilot information determining section 110 then outputs information onthe cyclic shift amounts and Walsh sequences of each stream to codingsection 101 and estimation section 108. Since cyclic shift amounts inthe second and subsequent streams are determined based on the cyclicshift amounts and offset information of the first stream, only cyclicshift amounts of the first stream may be inputted to coding section 101.Furthermore, since Walsh sequences of each stream are determined fromcyclic shift amounts of each stream, the Walsh sequences of each streamneed not be inputted to coding section 101.

The configuration of the terminal according to Embodiment 3 of thepresent invention is similar to the configuration of Embodiment 1 shownin FIG. 9 and is different only in some functions, and therefore onlydifferent functions will be described using FIG. 9.

Pilot information determining section 204 determines cyclic shiftamounts in the second and subsequent streams based on information oncyclic shift amounts of the first stream inputted from decoding section203 and offset information shared beforehand between the base stationand terminal. That is, the cyclic shift amounts in the second andsubsequent streams are determined by adding a fixed offset to the cyclicshift amounts of the first stream reported as control information. Forexample, when the offset information shown in pattern 1 of FIG. 20 isshared between the base station and terminal, if the cyclic shift amountused for the first stream (stream #0) from the base station is Δ0(Δ0<12), pilot information determining section 204 determines cyclicshift amount Δ1 used for the second stream (stream #1) to be (Δ0+6)mod12, determines cyclic shift amount Δ2 used for the third stream (stream#2) to be (Δ0+3)mod 12 and determines cyclic shift amount Δ3 used forthe fourth stream (stream #3) to be (Δ0+9)mod 12.

Furthermore, pilot information determining section 204 determines Walshsequences of each stream, based on the operating sequence identificationtable storing a correspondence relationship between a cyclic shiftamount and a Walsh sequence shared between the base station andterminal. That is, pilot information determining section 204 selectsWalsh sequences of each stream corresponding to determined cyclic shiftamounts Δ0, Δ1, Δ2 and Δ3 of each stream from the operating sequenceidentification table. Pilot information determining section 204 thenoutputs the determined cyclic shift amounts and Walsh sequences of eachstream to pilot signal generation section 205.

Next, the operating sequence identification table according to thepresent embodiment shown in FIG. 21 will be described.

First, when an offset amount, which is a difference between the cyclicshift amount of the first stream and the cyclic shift amount of thesecond stream is assumed to be ΔCS, a pair of cyclic shift amounts, aninterval of which is this offset amount ΔCS, will be considered. Forexample, when offset amount ΔCS is six, there are pairs of (0, 6), (2,8), (3, 9) and (4, 10). As shown in FIG. 21, in the present embodiment,cyclic shift amounts that form a pair are associated with the same Walshsequence.

Thus, when a cyclic shift amount distant by offset amount ΔCS from acyclic shift amount of the first stream is set as a cyclic shift amountof the second stream, cyclic shift amounts, an interval of which is ΔCS,are associated with the same Walsh sequence, and the first stream andsecond stream can thereby be set in the same Walsh sequence.

Furthermore, in the present embodiment, when groups (three types) areformed of cyclic shift sequences, an interval between cyclic shiftamounts of which is 3 (that is, ½ of maximum value “6” of the cyclicshift amount interval), the respective groups are associated with onlyWalsh sequence w1, only Walsh sequence w2 and both Walsh sequences w1and w2, respectively. For example, in the operating sequenceidentification table shown in FIG. 21, the group formed of cyclic shiftamounts “1, 4, 7, 10” is associated with only Walsh sequence w1.Furthermore, the group formed of cyclic shift amounts “2, 5, 8, 11” isassociated with only Walsh sequence w2. Furthermore, the group formed ofcyclic shift amounts “0, 3, 6, 9” is associated with two Walsh sequencesw1 and w2 respectively.

FIG. 22 is a diagram illustrating a correspondence relationship betweena cyclic shift amount and a Walsh sequence set in the second to fourthstreams when the operating sequence identification table shown in FIG.21 is used. As is clear from FIG. 22, when the base station reports anyone of cyclic shift amounts “0, 3, 6, 9” to the terminal, the first tofourth streams are associated with both Walsh sequences w1 and w2. Onthe other hand, when the base station reports any one of cyclic shiftamounts “1, 4, 7, 10” to the terminal, the first to fourth streams areassociated with only Walsh sequence w1. Furthermore, when the basestation reports any one of cyclic shift amounts “2, 5, 8, 11” to theterminal, the first to fourth streams are associated with only Walshsequence w2. In LTE, “1, 5, 7, 11” cannot be reported as cyclic shiftamounts, but by reporting cyclic shift amounts other than “1, 5, 7, 11,”the base station can set Walsh sequences of the first to fourth streams.

Thus, in the present embodiment, pilot information determining section110 and pilot information determining section 204 store a singleoperating sequence identification table that defines candidates forpairs of a cyclic shift amount of each cyclic shift sequence and a Walshsequence used for the first stream, and can thereby switch between Walshsequences in the second and subsequent streams according to cyclic shiftamounts of the first stream.

Furthermore, as is clear from FIG. 22, when transmission is performedwith two streams, the same Walsh sequence is set in the first stream andsecond stream irrespective of cyclic shift amounts. In the case of threeor more streams, it is observed that by selecting cyclic shift amountsof the first stream to be reported, it is possible to select whetherWalsh sequences used in the third and subsequent streams have the samesign as or a different sign from that of Walsh sequences used in thefirst and second stream. Pilot information determining section 110 andpilot information determining section 204 need only to store oneoperating sequence identification table indicating a “correspondencerelationship between a cyclic shift amount and a Walsh sequence” asshown in FIG. 21.

As described above, in the present embodiment, when offset amount ΔCS,which is a difference in cyclic shift amounts between the first streamand the second stream, is assumed to be fixed, in the operating sequenceidentification table, of a pair of cyclic shift amounts, which aredistant by offset amount ΔCS from each other, the same Walsh sequence isassociated with one cyclic shift amount and the other cyclic shiftamount that form the pair. Thus, the same Walsh sequence is set in thefirst stream and the second stream irrespective of cyclic shift amounts.

When offset amount ΔCS, which is a difference in cyclic shift amountsbetween the first stream and the second stream, is a maximum valuebetween the cyclic shift amounts, if cyclic shift amount groups, acyclic shift amount interval of which is ½ of offset amount ΔCS areformed, the respective cyclic shift amount groups are associated withonly a first Walsh sequence, only a second Walsh sequence and both thefirst and second Walsh sequences respectively. Thus, in the operatingsequence identification table, in a plurality of cyclic shift amountgroups formed of cyclic shift amounts, a cyclic shift amount interval ofwhich is ½ of a maximum value of the cyclic shift amount interval, theWalsh sequence associated with cyclic shift amounts included in thefirst cyclic shift amount group is a first Walsh sequence, the Walshsequence associated with cyclic shift amounts included in the secondcyclic shift amount group is a second Walsh sequence and the Walshsequences associated with cyclic shift amounts included in the thirdcyclic shift amount group are the first and second Walsh sequences.Thus, by selecting a cyclic shift amount of the first stream to bereported, it is possible to select whether the Walsh sequence used inthe third and subsequent streams should be a Walsh sequence having thesame sign as that of the Walsh sequence used in the first and secondstreams or a Walsh sequence having a different sign.

Thus, the present embodiment sets Walsh sequences in each stream usingone “correspondence relationship between a cyclic shift amount and aWalsh sequence” and the amount of offset in cyclic shift amounts betweenthe first stream and another stream. This eliminates the need forstoring an operating sequence identification table for every streamnumber (rank) and also eliminates the need for processing correspondingto the plurality of operating sequence identification tables, and canthereby reduce the circuit scale. That is, by arranging cyclic shiftamounts in the second and subsequent streams between the base stationand terminal, cyclic shift amounts in the second and subsequent streamsare determined by only reporting cyclic shift amounts of the firststream and Walsh sequences in each stream can be set using one“correspondence relationship between a cyclic shift amount and a Walshsequence,” which is independent of the stream number (rank), withrespect to this cyclic shift amount.

A case has been described above where the number of operating streams isfour and pilot signals are transmitted using four streams as an example,but even in a case where the number of operating streams is 2 or 3, theWalsh sequence of the second stream is assumed to have the same sign asthat of the Walsh sequence of the first stream and Walsh sequences inthe third and subsequent streams are assumed to have the same sign or adifferent sign. Furthermore, when the number of streams of pilot signalsis two or less, for example, when the number of transmission antennas istwo or less, pilot signals are transmitted with the same Walsh sequence.

Furthermore, the pattern in which a cyclic shift sequence is associatedwith a Walsh sequence may differ from one cell to another. Even in thesame cyclic shift sequence, Walsh sequences may be common or differentbetween cells and inter-sequence interference of pilot signals can berandomized (averaged) between cells.

Furthermore, the above-described pattern numbers may be associated withUE-specific information (UEID or the like), cell ID or the like. Thiseliminates the need for reporting correspondence relationship patterns,and can reduce the amount of reporting from the base station.

Furthermore, the operating sequence identification table with theabove-described patterns may be updated to a new operating sequenceidentification table by the base station reporting a new operatingsequence identification table through higher layer signaling. That is,the table need not be specified by a specification. This allows acorrespondence relationship pattern to be changed according toproportions of LTE terminals and LTE-A terminals.

A case has been described above where Walsh sequences are used inaddition to cyclic shift sequences, but the present invention is notlimited to Walsh sequences; the present invention is likewise applicableto any orthogonal sequence or sequence having a high level oforthogonality. For example, Walsh sequences may be substituted by OCC(Orthogonal Cover Code).

Furthermore, the Walsh sequence length is not limited to 2, but may beother sequence lengths.

Furthermore, assignment control information may also be referred to as“DCI (Downlink Control Information)” or “PDCCH.”

Furthermore, in Embodiment 1, the base station reports a correspondencerelationship (pattern) between a stream number and a Walsh sequence toeach terminal, but the base station may also report a Walsh sequence tobe used for the first stream to each terminal.

Although an antenna has been described in the aforementionedembodiments, the present invention may be similarly applied to anantenna port.

The antenna port refers to a logical antenna including a single or aplurality of physical antenna(s). That is, the antenna port is notlimited to a single physical antenna, but may refer to an array antennaincluding a plurality of antennas.

For example, in 3 GPP LTE, how many physical antennas are included inthe antenna port is not specified, but the minimum unit allowing thebase station to transmit different reference signals is specified.

In addition, the antenna port may be specified as a minimum unit formultiplying a weight of the pre-coding vector.

Also, although cases have been described with the above embodiment asexamples where the present invention is configured by hardware, thepresent invention can also be realized by software.

Each function block employed in the description of each of theaforementioned embodiments may typically be implemented as an LSIconstituted by an integrated circuit. These may be individual chips orpartially or totally contained on a single chip. “LSI” is adopted herebut this may also be referred to as “IC,” “system LSI,” “super LSI,” or“ultra LSI” depending on differing extents of integration.

Further, the method of circuit integration is not limited to LSI's, andimplementation using dedicated circuitry or general purpose processorsis also possible. After LSI manufacture, utilization of a programmableFPGA (Field Programmable Gate Array) or a reconfigurable processor whereconnections and settings of circuit cells within an LSI can bereconfigured is also possible.

Further, if integrated circuit technology comes out to replace LSI's asa result of the advancement of semiconductor technology or a derivativeother technology, it is naturally also possible to carry out functionblock integration using this technology. Application of biotechnology isalso possible.

The disclosure of Japanese Patent Application No. 2009-229649, filed onOct. 1, 2009 and Japanese Patent Application No. 2010-086141, filed onApr. 2, 2010, including the specification, drawings and abstract isincorporated herein by reference in its entirety.

INDUSTRIAL APPLICABILITY

The terminal station apparatus or the like according to the presentinvention is suitable for use as a terminal station apparatus or thelike that reduces inter-sequence interference in pilot signals betweenterminals while suppressing to a low level inter-sequence interferencein a plurality of pilot signals used by the same terminal even whenSU-MIMO and MU-MIMO are applied simultaneously.

REFERENCE CODES LIST

-   -   100 Base station    -   101, 207 Coding section    -   102, 208 Modulation section    -   103, 212 RF transmission section    -   104, 201 RF reception section    -   105 Separation section    -   106, 111 DFT section    -   107, 112 Demapping section    -   108 Estimation section    -   109 Scheduling section    -   110, 204 Pilot information determining section    -   113 Signal separation section    -   114 IFFT section    -   115, 202 Demodulation section    -   116, 203 Decoding section    -   117 Error detection section    -   200 Terminal    -   205 Pilot signal generation section    -   206 CRC section    -   209 Allocation section    -   210 Multiplexing section    -   211 Transmission power/weight control section

The invention claimed is:
 1. A terminal apparatus comprising: circuitry,which, in operation, generates a reference signal using a cyclic shiftvalue and an orthogonal sequence, which are associated with each other,the orthogonal sequence being one of two orthogonal sequencescorresponding to a first orthogonal sequence [1, 1] and a secondorthogonal sequence [1, −1], and the cyclic shift value being one of 12cyclic shift values ranging from 0 to 11; and a transmitter, which, inoperation, transmits the reference signal multiplexed with a datasignal, wherein two of the cyclic shift values having a difference of 6are respectively associated with the two orthogonal sequences.
 2. Theterminal apparatus according to claim 1, wherein in using the firstorthogonal sequence, the reference signal transmitted on a first slot ismultiplied by 1, and the reference signal transmitted on a second slotis multiplied by 1, and in using the second orthogonal sequence, thereference signal transmitted on the first slot is multiplied by 1, andthe reference signal transmitted on the second slot is multiplied by −1.3. The terminal apparatus according to claim 1, wherein the transmitter,in operation, transmits the reference signal multiplexed with the datasignal having a bandwidth, which is different from a bandwidth of a datasignal transmitted by another terminal apparatus.
 4. The terminalapparatus according to claim 1, wherein the circuitry, in operation,generates the reference signal using the orthogonal sequence, which isassociated with one of a plurality of layer numbers by an association inwhich: a first layer and a second layer are associated with a first oneof the two orthogonal sequences; and a third layer and a forth layer areassociated with a second one of the two orthogonal sequences.
 5. Theterminal apparatus according to claim 1, wherein the circuitry, inoperation, generates the reference signal using the orthogonal sequence,which is associated with one of a plurality of layer numbers by anassociation in which: a first to a Nw-th layer(s) are associated with afirst one of the two orthogonal sequences; and a (Nw+1)-th andsubsequent layer(s) are associated with a second one of the twoorthogonal sequences, wherein Nw is a positive integer.
 6. The terminalapparatus according to claim 5, wherein the Nw is variable.
 7. Theterminal apparatus according to claim 5, wherein a number of the layersis 4, and the Nw is 2 or
 4. 8. The terminal apparatus according to claim1, wherein the circuitry, in operation, generates the reference signalusing the cyclic shift value, which is associated with one of aplurality of layer numbers by an association in which: a differencebetween the cyclic shift values, with which a first layer and a secondlayer are respectively associated, is 6; a difference between the cyclicshift values, with which a third layer and a fourth layer arerespectively associated, is 6; and a difference between the cyclic shiftvalues, with which the first layer and the third layer are respectivelyassociated, is
 3. 9. The terminal apparatus according to claim 1,wherein a number of the cyclic shift values associated with the firstorthogonal sequence is same as a number of the cyclic shift valuesassociated with the second orthogonal sequence.
 10. The terminalapparatus according to claim 1, wherein the circuitry, in operation,generates the reference signal using the cyclic shift value and theorthogonal sequence, which are associated with each other by anassociation in which two adjacent ones of the cyclic shift values arerespectively associated with the two orthogonal sequences.
 11. Acommunication method comprising: generating a reference signal using acyclic shift value and an orthogonal sequence, which are associated witheach other, the orthogonal sequence being one of two orthogonalsequences corresponding to a first orthogonal sequence [1, 1] and asecond orthogonal sequence [1, −1], and the cyclic shift value being oneof 12 cyclic shift values ranging from 0 to 11; and transmitting thereference signal multiplexed with a data signal, wherein two of thecyclic shift values having a difference of 6 are respectively associatedwith the two orthogonal sequences.
 12. The communication methodaccording to claim 11, wherein in using the first orthogonal sequence,the reference signal transmitted on a first slot is multiplied by 1, andthe reference signal transmitted on a second slot is multiplied by 1,and in using the second orthogonal sequence, the reference signaltransmitted on the first slot is multiplied by 1, and the referencesignal transmitted on the second slot is multiplied by −1.
 13. Thecommunication method according to claim 11, wherein the transmittingincludes transmitting the reference signal multiplexed with the datasignal having a bandwidth, which is different from a bandwidth of a datasignal transmitted by another terminal.
 14. The communication methodaccording to claim 11, wherein the generating includes generating thereference signal using the orthogonal sequence, which is associated withone of a plurality of layer numbers by an association in which: a firstlayer and a second layer are associated with a first one of the twoorthogonal sequences; and a third layer and a forth layer are associatedwith a second one of the two orthogonal sequences.
 15. The communicationmethod according to claim 11, wherein the generating includes generatingthe reference signal using the orthogonal sequence, which is associatedwith one of a plurality of layer numbers by an association in which: afirst to a Nw-th layer(s) are associated with a first one of the twoorthogonal sequences; and a (Nw+1)-th and subsequent layer(s) areassociated with a second one of the two orthogonal sequences, wherein Nwis a positive integer.
 16. The communication method according to claim15, wherein the Nw is variable.
 17. The communication method accordingto claim 15, wherein a number of the layers is 4, and the Nw is 2 or 4.18. The communication method according to claim 11, wherein thegenerating includes generating the reference signal using the cyclicshift value, which is associated with one of a plurality of layernumbers by an association in which: a difference between the cyclicshift values, with which a first layer and a second layer arerespectively associated, is 6; a difference between the cyclic shiftvalues, with which a third layer and a fourth layer are respectivelyassociated, is 6; and a difference between the cyclic shift values, withwhich the first layer and the third layer are respectively associated,is
 3. 19. The communication method according to claim 11, wherein anumber of the cyclic shift values associated with the first orthogonalsequence is same as a number of the cyclic shift values associated withthe second orthogonal sequence.
 20. The communication method accordingto claim 11, wherein the generating includes generating the referencesignal using the cyclic shift value and the orthogonal sequence, whichare associated with each other by an association in which two adjacentones of the cyclic values are respectively associated with the twoorthogonal sequences.